AP390 mesh problems

I am having trouble getting an AP390 to mesh up with an AP1130. The 390 has 5 small external antennas, and one 5ghz omni attached. The 390's are inside a mobile classroom. The omni antenna is connected to 5ghz (1) and runs through the wall to a bracket above the roof. The antenna is about 45 feet away (horizontal) from the 1130, and down about 2 or 3 feet in elevation. When the ap is connected via ethernet, it works fine. When we place it in the mobile and boot it up, it takes between 20 and 25 minutes before it connects to the one premise HM. I have changed the 390 with a spare unit, and have the same issue. I have plugged the antenna into my Wi-Spy device, and can see the 1130 with a -33 signal. when I console into the AP, it is showing the client ip as a 192.168 and we use a 10. schema at all of our sites. After it finally connects, it gets a dhcp in our proper 10 scheme. I am wondering if maybe there is a way to set the radio profile to force it to look at the omni. I am suspecting that it is meshing up via one of the standard antennas instead of the larger omni. How can I tell??